Patterns for Emmett

Emmett is crafted to fit the needs of many applications, from the smallest to the largest ones. Due to this, your application can be built up from a single Python file and scale to a better organized structure.

In this section, we will cover some good patterns you may follow when your application starts becoming large, or when you just need to organize your code better.

Package pattern

The package pattern will make your application a Python package instead of a module. For instance, let's assume your original application is structured like that:

/myapp
    myapp.py
    /static
        style.css
    /templates
        layout.html
        index.html
        login.html
        ...

To convert it to a package application, you should create another folder inside your original myapp one, and rename myapp.py to __init__.py, ending up with something like this:

/myapp
    /myapp
        __init__.py
        /static
            style.css
        /templates
            layout.html
            index.html
            login.html
            ...

– OK, dude. But what did we gain by doing this?
– well, now we can organize the code in multiple modules

With this new structure, we can create a new views.py file inside the package and we can move the routed functions to it. For example, your __init__.py file can look like this:

from emmett import App

app = App(__name__)

from . import views

and your views.py could look like:

from . import app

@app.route("/")
async def index():
    # some code

Your final structure would be like this:

/myapp
    /myapp
        __init__.py
        views.py
        /static
            style.css
        /templates
            layout.html
            index.html
            login.html
            ...

– That's nice, but how can I run my application now?

You can use the Emmett command inside the original directory of your application:

$ emmett -a myapp develop

A note regarding circular imports:
Every Python developer hates them, and yet we just added some of them: views.py depends on __init__.py while __init__.py imports views.py. In general, this is a bad idea, but it is actually fine here because we are not actually using the views in __init__.py. We are ensuring that the module is imported to expose the functions; also, we are doing that at the bottom of the file.

MVC pattern

The MVC (Model-View-Controller) pattern, used widely in web applications, is well structured and becomes handy when you have big applications. Emmett does not provide controllers, but you can implement an MVC pattern using application modules. An MVC structure for an Emmett application can look something like this:

/myapp
    __init__.py
    /controllers
        __init__.py
        main.py
        api.py
    /models
        __init__.py
        user.py
        article.py
    /templates
        layout.html
        index.html
        login.html
        ...

As you can see, it's an extension of the package pattern, where we added the two sub-packages controllers and models, each with an empty __init__.py file.

With this structure, your application's __init__.py would look like this:

from emmett import App
from emmett.orm import Database

app = App(__name__)
app.config.url_default_namespace = "main"

db = Database()

from .models.user import User
from .models.article import Post
db.define_models(User, Post)

from .controllers import main, api

We told Emmett to use the main.py controller as default for urls, so we can just call url('index') instead of url('main.function') in our application.

The main controller can look like this:

from .. import app

@app.route("/")
async def index():
    # code

and the api.py controller can look like this:

from .. import app

api = app.module(__name__, 'api', url_prefix='api')

@api.route()
async def a():
    # code